1. Field of the Invention
The present invention relates to systems, i.e. methods of and apparatus for evaporating liquids. The invention has particular utility for use in connection with the evaporation of the water portion of water-based liquid wastes and will be described in connection with such utility, although other utilities are contemplated. More particularly, the present invention is directed to systems for converting portions of the liquid to environmentally safe vapors while concurrently separating the various other constituents such as oils and solids resident in the liquid. The primary objective is a safe and economical method and apparatus to reduce the disposal volume and therefore the escalating costs and liabilities associated with the disposal of water-based liquid wastes.
Current environmental pressures are forcing industry to find more satisfactory and economical methods of dealing with their increasingly regulated water-based wastes, other than putting them down the drain or shipping them off-site. Ever tightening sewer regulations are eliminating the "to drain" method as an option. Shipping wastes off-site incurs both high costs and ongoing legal liabilities.
2. Description of the Prior Art
A variety of methods have been proposed to address the disposal of contaminated waters, such as filtration or chemical treatment. However, each of these methods has certain operational drawbacks, economic restraints, and inabilities to meet new and anticipated regulatory limitations. Evaporators of various designs also have been proposed to address disposal of contaminated waters. While not eliminating the disposal problems entirely, evaporators have the advantage of reducing the bulk, thus facilitating subsequent handling. However, many prior art evaporators tend to be large in size, expensive in cost, complex and not geared toward handling the remaining oils, solids and/or sludge generated by the new type of applications.
More recently there has been proposed a generation of relatively small evaporators designed for on-site installation. See, for example, Erickson et al, U.S. Pat. No. 4,534,828 and the water evaporator earlier marketed by Samsco, Inc. as described in its bulletin "The Nordale Fluid Eliminator", 1988. While the Nordale Fluid Eliminator marketed by Samsco, Inc. has achieved a certain degree of commercial success, commercial acceptance has been less than overwhelming due to certain design deficiencies of the Nordale unit. For one, the Nordale unit is subject to uncontrolled variables which may negatively affect the efficiency of the operation and consistency in results. These uncontrolled variables also can create costly maintenance requirements, and may give rise to certain fire safety hazards.
The present invention overcomes the foregoing and other problems inherent in the Nordale unit. It overcomes the attendant inconsistencies in the safety, efficiency and performance of the Nordale unit and the resulting costly maintenance and operation problems experienced.
Referring to FIG. 1 of the drawings, which corresponds to FIG. 1 of Erickson et al, U.S. Pat. No. 4,534,828, there is shown a prior art evaporator as described in the aforesaid Erickson et al patent. The apparatus comprises a rectangular container or tank 111 for holding a fluid. Tank 111 includes a heater 117 for supplying heat, and is positioned adjacent the bottom 116 of the tank. Tank 111 includes an air inlet 132 adjacent the top front end 112 and an outlet opening 173 in the tank top 115 adjacent the tank back end 113. A suction blower fan 120 pulls air into the fluid-containing tank 111. A pivoting floating baffle mechanism indicated generally at 119 forces air to flow adjacent the surface of the liquid contained in the tank 111. Initially air/oxygen is drawn through the burner assembly 150 where the air/oxygen mixes with the fuel to provide combustion. The resulting gaseous stream is comprised of burner gases. Secondly, ambient air is drawn into the tank 111 and across the surface of the heated fluid via opening 132 in the tank, whereby to pick up water vapor overhead. The two exhaust gas streams, comprised of burner gases and water vapor-air, are drawn from the tank through a common lid exhaust opening 132 and into a continuation draft diverter extension 180. The smaller diameter burner tube exit 172 is positioned in the center of the larger diameter exhaust opening 173 and continuing draft diverter 180. This is so positioned relative to the exhaust opening in order that a perfect annulus configuration is provided. The water vapor-air stream forms the outer ring of the annulus, and the hot flue gases form the inner ring of the annulus. Both streams flow in the same direction, one surrounding the other.
According to Erickson et al, the velocity of the hot flue gases aspirate the outer annular air/vapor stream along with it, as the two streams exit the tank through the one exhaust opening. In practice, it has been observed that fluctuations in operational variables can affect the gas/oxygen ratio equilibrium. Such fluctuations change the air/oxygen flow through the burner and burner tube, while the gas volume remains constant. This can result in deleterious inconsistencies and air flow complexities, including periods of incomplete combustion or excess air, due to an insufficient or excessive air-to-gas ratio respectively.
When the lid of such prior evaporation tanks is opened, there are changes in the air flow being drawn into the tank. These can dramatically change the air characteristics of the air/vapor stream flowing by the burner tube and thus the characteristics of the combustion gas/air flow being drawn through the burner and burner tube. This creates the danger of sudden flashback through the burner, which can lead to extinguishing the burner flame. Such undesired shutting down results in production losses until it is discovered, requiring re-starting with its attendant maintenance and labor cost.
If the operation continues running with the lid up, the burner can run rich and will have incomplete combustion. This can cause maintenance problems and seriously reduced efficiency. Soot frequently coats the inside of the burner tube, insulating it and allowing the heat to go up the stack rather than being transferred through the heat exchanger to the liquid as required. Soot also may clog the burner tube exit, which, causes the burner to burn even more inefficiently and creates a cycle of worsening conditions, producing additional sooting. This in turn causes even richer gas mixtures, with continuing loss of efficiency, increased cost of operation, production downtime, and maintenance costs to remove the accumulated soot.
These prior designs provide the operator only a crude fixed cast device with holes for adjusting and matching air/oxygen input with gas volume input, so as to maintain a constant ratio at any BTU level. To change the air/oxygen volume to match changes in the gas volume, the operator is required either to increase hole diameters by drilling or reduce hole diameters by placing bolts in existing holes. Such designs do not provided a simple, controllable or other way to access the correctness of such combustion air adjustments. It must be checked by looking down the tube and visually assessing the color, length and brightness of the flame as air volume changes.